This invention relates to tapered roller bearings and gear shaft support devices for vehicles.
Tapered roller bearings are suitable to support radial load, axial load and combined load. Because of their large load capacity, they are used to support gear shafts of power transmission devices such as differentials and transmissions in automobiles and construction machines.
FIG. 1 shows an automotive differential in which a gear shaft is supported by tapered roller bearings which is one of the embodiments of the present invention. It basically comprises a drive pinion 4 rotatably supported in a housing 1 by two tapered roller bearings 2, 3, a ring gear 5 meshing with the drive pinion 4, a differential gear case 7 carrying the ring gear 5 and rotatably supported in the housing 1 by a pair of tapered roller bearings 6, pinions 8 mounted in the differential gear case 7, and a pair of side gears 9 meshing with the pinions 8. These members are mounted in the housing 1 in which is sealed gear oil. The gear oil also serves as a lubricating oil for the tapered roller bearings 2, 3, 6.
FIG. 10 shows one conventional type of tapered roller bearing. It comprises an outer ring 52 having a conical raceway 51, an inner ring 56 having a conical raceway 53, a large rib surface 54 on the large-diameter side of the raceway 53 and a small rib surface 55 on its small-diameter side, a plurality of tapered rollers 57 rollably arranged between the raceway 51 of the outer ring 52 and the raceway 53 of the inner ring 56, and a retainer 58 keeping the tapered rollers 57 circumferentially spaced a predetermined distance from each other. The distance between the large rib surface 54 and the small rib surface 55 of the inner ring is designed to be slightly longer than the length of the tapered rollers 57.
The tapered rollers 57 are designed to come into line contact with the raceways 51 and 53 of the outer ring 52 and the inner ring 56 with the cone apexes of the tapered rollers 57 and the raceways 51, 53 converging on a point O on the centerline of the tapered roller bearing. By this arrangement, the tapered rollers 57 can roll along the raceways 51, 53.
With such a tapered roller bearing, the raceways 51, 53 have different cone angles, so that the combined force of loads applied to the tapered rollers 57 from the raceways 51, 53 acts in such a direction as to push the tapered rollers 57 toward the large rib surface 54 of the inner ring 56. Thus, during use of the bearing, the tapered rollers 57 are guided with their large end faces 59 pressed against the large rib surface 54, so that the large end faces 59 and the large rib surface 54 are in sliding contact with each other.
On the other hand, since the distance between the large rib surface 54 and the small rib surface 55 is designed to be slightly longer than the length of the tapered rollers 57, as shown enlarged in FIG. 11, the small rib surface 55 does not contact the small end faces 60 of the tapered rollers 57 such that small clearances exist therebetween. Also, the small rib surface 55 is formed by a surface inclined outwardly relative to the small end faces 60 of the tapered rollers 57. In the bearing manufacturing steps, the small rib surface 55 and the small end faces 60, which are kept out of contact with each other, are not finished by grinding.
In mounting such a tapered roller bearing in a mounting position, as shown in FIG. 12A, the assembly comprising the inner ring 56, the tapered rollers 57 and the retainer 58 is inserted into the raceway 51 of the outer ring 52 from above with the large end faces 59 of the tapered rollers 57 facing up. At this time, since the tapered rollers 57 have freedom relative to the inner ring 56 and the retainer 58, they will not seat in position, and their small end faces 60 are brought into contact with the small rib surface 55. This is an initial assembled state in which clearance δ is present between the large end faces 59 and the large rib surface 54 of the inner ring 56.
Next, the tapered roller bearing in the initial assembled state is temporarily mounted on a mounting position of a mating device. As shown in FIG. 12B, when break-in is carried out at a low speed of about 50–100 rpm while applying an axial load Fa to the end face of the inner ring 56, the tapered rollers 57 will move a distance equal to the gap δ toward the large rib surface 54, until as shown in FIG. 12C, the large end faces 59 come into contact with the large rib surface 54 of the inner ring 56, so that they settle at a regular position during use of the bearing where a gap δ exists between the small end face 60 and the small rib surface 55.
Thereafter, the tapered roller bearing is preloaded axially under a predetermined load. This preloading is carried out to prevent axial movement of the tapered rollers 57 during use of the bearing, and to stably bring the tapered rollers into line contact with the raceways 51, 53 of the outer ring 52 and the inner ring 56. The control of preloading force is carried out by measuring the shaft torque, and preloading ends when the shaft torque reaches a predetermined value.
Since the power transmission device such as a differential has many gear meshing portions and sliding portions of rotary members, foreign matter such as metallic powder produced by wear at these portions can enter gear oil sealed in the housing. Such powder will penetrate into tapered roller bearings for supporting gear shafts, which are rotating under high load, thus shortening the working life of the tapered roller bearings.
Also, when such tapered roller bearings are used to support gear shafts of a differential which rotates at high speed under high load, since the large end faces of the tapered rollers are brought into sliding contact with the large rib surface of the inner ring, torque due to the slide contact increases. Further, due to frictional heat buildup, the temperature of the bearing portion will rise, thus lowering the viscosity of gear oil. This may cause shortage of oil film.
Further, in mounting the tapered roller bearing on a mounting portion, if the gap between the large end faces 59 of the tapered rollers 57 and the large rib surface 54 is large in the initial assembled state shown in FIG. 12A, break-in time tends to be long until the tapered rollers 57 settle in their regular positions shown in FIG. 12C. As shown in FIG. 11, since the small rib surface 55 of the inner ring 56 is formed inclined outwardly relative to the small end faces 60 of the tapered rollers 57, variation in the gap between the large end faces 59 and the large rib surface 54 in the initial assembled state is large for the following reasons, and the abovementioned break-in time until all the tapered rollers 57 settle in their regular positions tends to become even longer.
Generally, the small end faces of the tapered rollers remain as forged surfaces, so that chamfer dimensions and shape are large in variation. Variations in chamfer dimension and shape are present not only between tapered rollers but in a circumferential direction of one tapered roller. As shown by solid and chain lines in FIG. 11, if the chamfer dimension and shape of the small end faces 60 differ from each other, the following will result. In the case of the small end faces 60 shown by solid line, in the initial assembled state, point P1 on the small end face 60 comes into contact with point Q1 on the small rib surface 55, so that the gap δ when the tapered rollers 57 settle will be δ1. On the other hand, in the case of the small end face 60 shown by chain line, in the initial assembled state, point P2 comes into contact with point Q2, so that the gap δ when the tapered rollers 57 settle will be δ2. Thus, due to differences in chamfer dimension and shape of the small end faces 60, the time until each tapered roller 57 settles in position tends to vary, so that longer break-in time is required.
An object of this invention is to ensure a long endurance life for a tapered roller bearing and a gear shaft support device for a vehicle.
Another object is to reduce torque loss and heat buildup due to friction.
A further object is to shorten break-in time.